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scx_layered: Add helper for layer slice duration #918

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Nov 11, 2024
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scx_layered: Add helper for layer slice duration #918

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35 changes: 20 additions & 15 deletions scheds/rust/scx_layered/src/bpf/main.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,11 @@ static struct layer *lookup_layer(int idx)
return &layers[idx];
}

static __always_inline u64 layer_slice_ns(struct layer *layer)
{
return layer->slice_ns > 0 ? layer->slice_ns : slice_ns;
}

static __always_inline
int rotate_layer_id(u32 base_layer_id, u32 rotation)
{
Expand Down Expand Up @@ -776,8 +781,8 @@ s32 BPF_STRUCT_OPS(layered_select_cpu, struct task_struct *p, s32 prev_cpu, u64

if (cpu >= 0) {
lstat_inc(LSTAT_SEL_LOCAL, layer, cctx);
u64 layer_slice_ns = layer->slice_ns > 0 ? layer->slice_ns : slice_ns;
scx_bpf_dispatch(p, SCX_DSQ_LOCAL, layer_slice_ns, 0);
u64 slice_ns = layer_slice_ns(layer);
scx_bpf_dispatch(p, SCX_DSQ_LOCAL, slice_ns, 0);
return cpu;
} else {
return prev_cpu;
Expand Down Expand Up @@ -1066,7 +1071,7 @@ void BPF_STRUCT_OPS(layered_enqueue, struct task_struct *p, u64 enq_flags)

try_preempt_first = cctx->try_preempt_first;
cctx->try_preempt_first = false;
u64 layer_slice_ns = layer->slice_ns > 0 ? layer->slice_ns : slice_ns;
u64 slice_ns = layer_slice_ns(layer);

if (cctx->yielding) {
lstat_inc(LSTAT_YIELD, layer, cctx);
Expand All @@ -1086,8 +1091,8 @@ void BPF_STRUCT_OPS(layered_enqueue, struct task_struct *p, u64 enq_flags)
* Limit the amount of budget that an idling task can accumulate
* to one slice.
*/
if (vtime_before(vtime, layer->vtime_now - layer_slice_ns))
vtime = layer->vtime_now - layer_slice_ns;
if (vtime_before(vtime, layer->vtime_now - slice_ns))
vtime = layer->vtime_now - slice_ns;

/*
* Special-case per-cpu kthreads which aren't in a preempting layer so
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I think this could potentially change the slice duration here as slice_ns variable is reused for kthreads. However, it should get set to the appropriate layers slice_ns vs the default which I think is reasonable.

Expand Down Expand Up @@ -1138,13 +1143,13 @@ void BPF_STRUCT_OPS(layered_enqueue, struct task_struct *p, u64 enq_flags)

if (disable_topology) {
tctx->last_dsq = tctx->layer;
scx_bpf_dispatch_vtime(p, tctx->layer, layer_slice_ns, vtime, enq_flags);
scx_bpf_dispatch_vtime(p, tctx->layer, slice_ns, vtime, enq_flags);
} else {
u32 llc_id = cpu_to_llc_id(tctx->last_cpu >= 0 ? tctx->last_cpu :
bpf_get_smp_processor_id());
idx = layer_dsq_id(layer->idx, llc_id);
tctx->last_dsq = idx;
scx_bpf_dispatch_vtime(p, idx, layer_slice_ns, vtime, enq_flags);
scx_bpf_dispatch_vtime(p, idx, slice_ns, vtime, enq_flags);
}

preempt:
Expand All @@ -1166,9 +1171,9 @@ static bool keep_running(struct cpu_ctx *cctx, struct task_struct *p)
if (!(tctx = lookup_task_ctx(p)) || !(layer = lookup_layer(tctx->layer)))
goto no;

u64 layer_slice_ns = layer->slice_ns > 0 ? layer->slice_ns : slice_ns;
u64 slice_ns = layer_slice_ns(layer);
/* @p has fully consumed its slice and still wants to run */
cctx->ran_current_for += layer_slice_ns;
cctx->ran_current_for += slice_ns;

/*
* There wasn't anything in the local or global DSQ, but there may be
Expand All @@ -1193,7 +1198,7 @@ static bool keep_running(struct cpu_ctx *cctx, struct task_struct *p)
*/
if (disable_topology) {
if (!scx_bpf_dsq_nr_queued(layer->idx)) {
p->scx.slice = layer_slice_ns;
p->scx.slice = slice_ns;
lstat_inc(LSTAT_KEEP, layer, cctx);
return true;
}
Expand All @@ -1202,7 +1207,7 @@ static bool keep_running(struct cpu_ctx *cctx, struct task_struct *p)
tctx->last_cpu :
bpf_get_smp_processor_id());
if (!scx_bpf_dsq_nr_queued(dsq_id)) {
p->scx.slice = layer_slice_ns;
p->scx.slice = slice_ns;
lstat_inc(LSTAT_KEEP, layer, cctx);
return true;
}
Expand All @@ -1229,7 +1234,7 @@ static bool keep_running(struct cpu_ctx *cctx, struct task_struct *p)
scx_bpf_put_idle_cpumask(idle_cpumask);

if (has_idle) {
p->scx.slice = layer_slice_ns;
p->scx.slice = slice_ns;
lstat_inc(LSTAT_KEEP, layer, cctx);
return true;
}
Expand Down Expand Up @@ -2059,11 +2064,11 @@ void BPF_STRUCT_OPS(layered_stopping, struct task_struct *p, bool runnable)
cctx->current_preempt = false;
cctx->prev_exclusive = cctx->current_exclusive;
cctx->current_exclusive = false;
u64 layer_slice_ns = layer->slice_ns > 0 ? layer->slice_ns : slice_ns;
u64 slice_ns = layer_slice_ns(layer);

/* scale the execution time by the inverse of the weight and charge */
if (cctx->yielding && used < layer_slice_ns)
used = layer_slice_ns;
if (cctx->yielding && used < slice_ns)
used = slice_ns;
p->scx.dsq_vtime += used * 100 / p->scx.weight;
cctx->maybe_idle = true;
}
Expand Down